The present invention relates to a method of controlling an automotive engine and in particular to a method of smoothing engine shutdown.
Some automotive vehicle powertrains incorporate engine start/stop (ESS) systems to improve fuel economy. ESS shuts down an internal combustion engine under specified conditions when engine torque is not required and restarts the engine when torque is again required. For example, ESS may shutdown the engine of a vehicle after a driver brakes the vehicle to a stop and then restart the engine when the driver requests torque by depressing an accelerator pedal. ESS is commonly incorporated into hybrid electric powertrains. In general, the more conditions specified when ESS will shutdown the vehicle engine, the greater the improvement to fuel economy.
However, noise, vibration, and harshness may result from the engine shutdown as an engine speed falls through a resonance frequency of the engine. Harshness may also result from energy being transferred, as the engine speed decreases, through the engine mounts to the vehicle.